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Help with existing system

I've owned my home for a couple of years now and I'd like to get a handle on my sprinkler system. I have spotty coverage and several good sized dry spots.

I have about 2/3 acre (basically flat) to water. I live in Colorado so wind and evaporation rates are important

Let me state what I think the problem is and hopefully you guys can jump in and start me on the road to recovery...

I don't know a lot about the main lines. I do know they are 1" and that I have 12 zones, each with 5-6 rotor heads. The heads are a mix of brands and nozzles (Orbit and Rain Bird). They are all 3/4" housings. Last year I fiddled with the "break up" screws to try to get better coverage but I only made things worse. This year I've done more research and I've reset all my heads so the "break up" screws are out of the stream. I do have head-to-head coverage (head spacing is 24'-30') but I do not have square or triangular configurations that give optimal overlap - that's one problem. The other bigger problem is water pressure. My static pressure is 45 PSI. I measured at one of ports on the the anti-siphon valve. I have not calculated pressure loss yet but using the same gauge in the same port, I've observed that my pressure is around 15-18 PSI while the system is operating. I'm pretty sure the pressure is marginal at best for my rotor heads. One zone will not "pop-up" on it's own (I can push on a partially open head and get it running) and the other zones function but I suspect the pattern is bad due to low pressure.

My water supply is a 3/4" PEX line and the sprinkler system is fed off of the main line before the pressure regulator. I haven't measured GPM yet.

I'm willing to dig up and replace heads and/or replace nozzles and I'll add a booster pump if it'll help, but I don't have any interest in adding heads/zones.

Don't go removing pressure regulators. Street pressures in Colorado neighborhoods can be off the charts, because of the elevations they have. One could attempt to adjust a regulator to bring up the outlet pressure a bit.

Why would they regulate a home that has static 45psi?
At any rate, the system branches off before the regulator, so the regulator isn't a factor. I'm more concerned with the size piping that exits the house. If they continued out of the house with 3/4", then the flow for the system should have been designed closer to 9-10gpm. 5-6 rotors per zone seems excessive for a 3/4" supply. I would calculate the zone's GPM recquirement before going any further. Look at the nozzle of each rotor and add up the numbers.

I didn't know I could shut the flow off on my heads (RB 5000 Plus). So I experimented a bit by shutting off the flow to all but 2 heads. Quite a difference... the droplet pattern out of the heads is much more what I expect to see - good even distribution. I then turned the flow back on one head at a time. Once I got up to 5 heads running the droplet pattern was pretty poor - more of a pencil stream coming out. I still get 27' or so but the distribution is poor.

All of that was with the nozzles that are currently in the heads.

So I'm going to replace them all w/ 1.5s and hopefully that will do the trick.